Color stable red-emitting phosphors

ABSTRACT

A process for preparing a Mn +4  doped phosphor of formula I 
       A x [MF y ]:Mn +4    I
 
     includes gradually adding a first solution to a second solution gradually discharging the product liquor from the reactor while volume of the product liquor in the reactor remains constant;
 
wherein
         A is Li, Na, K, Rb, Cs, or a combination thereof;   M is Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Y, La, Nb, Ta, Bi, Gd, or a combination thereof;   x is the absolute value of the charge of the [MF y ] ion;   y is 5, 6 or 7.
 
The first solution includes a source of M and HF and the second solution includes a source of Mn to a reactor in the presence of a source of A.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a non-provisional of and claims priority from U.S.provisional application, Ser. No. 62/118,703, filed Feb. 20, 2015, theentire disclosure of which is incorporated herein by reference.

BACKGROUND

Red-emitting phosphors based on complex fluoride materials activated byMn⁴⁺, such as those described in U.S. Pat. No. 7,358,542, U.S. Pat. No.7,497,973, and U.S. Pat. No. 7,648,649, can be utilized in combinationwith yellow/green emitting phosphors such as YAG:Ce to achieve warmwhite light (CCTs<5000 K on the blackbody locus, color rendering index(CRI)>80) from a blue LED, equivalent to that produced by currentfluorescent, incandescent and halogen lamps. These materials absorb bluelight strongly and efficiently emit in a range between about 610 nm and658 nm with little deep red/NIR emission. Therefore, luminous efficacyis maximized compared to red phosphors that have significant emission inthe deeper red where eye sensitivity is poor. Quantum efficiency canexceed 85% under blue (440-460 nm) excitation. In addition, use of thered phosphors for displays can yield high gamut and efficiency.

Processes for preparing the materials described in the patent andscientific literature typically involve mixing the raw materials andprecipitating the product. Some examples of such batch processes aredescribed in Paulusz, A. G., J. Electrochem. Soc., 942-947 (1973), U.S.Pat. No. 7,497,973, and U.S. Pat. No. 8,491,816. However, scale-upissues and batch to batch variation of properties of the product can bea significant problem. Moreover, batch processes produce materialshaving a broad range of particles sizes including relatively largeparticles. Large particles may clog dispensing equipment, causingproblems in manufacturing LED packages, and also tend to settleunevenly, resulting in, non homogeneous distribution. Therefore,processes for preparing the red phosphor that can yield a product havinga smaller median particle size and a narrower particle sizedistribution, and allow better control over the final properties of theproduct, while maintaining performance in lighting and displayapplications, are desirable.

BRIEF DESCRIPTION

Briefly, in one aspect, the present invention relates to processes forsynthesizing a Mn⁴⁺ doped phosphor of formula I

A_(x)[MF_(y)]:Mn⁺⁴   I

-   -   wherein    -   A is Li, Na, K, Rb, Cs, or a combination thereof;    -   M is Si, Ge, Sn. Ti, Zr, Al, Ga, In, Sc, Y, La, Nb, Ta, Bi, Gd,        or a combination thereof;    -   x is the absolute value of the charge of the [MF_(y)] ion; and    -   y is 5, 6 or 7.

The process includes gradually adding a first solution comprising asource of M and HF and a second solution comprising a source of Mn to areactor in the presence of a source of A, to form a product liquorcomprising the Mn⁺⁴ doped phosphor; and gradually discharging theproduct liquor from the reactor; wherein volume of the product liquor inthe reactor remains constant.

In another aspect, the present invention relates to Mn⁴⁺ doped phosphorsof formula I.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a schematic cross-sectional view of a lighting apparatus inaccordance with one embodiment of the invention;

FIG. 2 is a schematic cross-sectional view of a lighting apparatus inaccordance with another embodiment of the invention;

FIG. 3 is a schematic cross-sectional view of a lighting apparatus inaccordance with yet another embodiment of the invention;

FIG. 4 is a cutaway side perspective view of a lighting apparatus inaccordance with one embodiment of the invention;

FIG. 5 is a schematic perspective view of a surface-mounted device (SMD)backlight LED.

DETAILED DESCRIPTION

The Mn⁴⁺ doped phosphors of formula I are complex fluoride materials, orcoordination compounds, containing at least one coordination center,surrounded by fluoride ions acting as ligands, and charge-compensated bycounter ions as necessary. For example, K₂SiF⁶:Mn⁺⁴, the coordinationcenter is Si and the counterion is K. Complex fluorides are occasionallywritten as a combination of simple, binary fluorides but such arepresentation does not indicate the coordination number for the ligandsaround the coordination center. The square brackets (occasionallyomitted for simplicity) indicate that the complex ion they encompass isa new chemical species, different from the simple fluoride ion. Theactivator ion (Mn⁴⁺) also acts as a coordination center, substitutingpart of the centers of the host lattice, for example, Si. The hostlattice (including the counter ions) may further modify the excitationand emission properties of the activator ion.

In particular embodiments, the coordination center of the phosphor, thatis, M in formula I, is Si, Ge, Sn, Ti, Zr, or a combination thereof.More particularly, the coordination center is Si, Ge, Ti, or acombination thereof, and the counterion, or A in formula I, is Na, K,Rb, Cs, or a combination thereof, and y is 6. Examples of phosphors offormula I include Examples of phosphors of formula I includeK₂[SiF₆]:Mn⁴⁺, K₂[TiF₆]:Mn⁴⁺, K₂[SnF₆]:Mn⁴⁺, Cs₂[TiF₆], Rb₂[TiF₆],Cs₂[SiF₆], Rb₂[SiF₆], Na₂[TiF₆]:Mn⁴⁺, Na₂[ZrF₆]:Mn⁴⁺, K₃[ZrF₇]:Mn⁴⁺,K₃[BiF₆]:Mn⁴⁺, K₃[YF₆]:Mn⁴⁺, K₃[LaF₆]:Mn⁴⁺, K₃[GdF₆]:Mn⁴⁺,K₃[NbF₇]:Mn⁴⁺, K₃[TaF₇]:Mn⁴⁺. In particular embodiments, the phosphor offormula I is K₂SiF₆:Mn⁴⁺.

The amount of manganese in the Mn⁺⁴ doped phosphors of formula I mayrange from about 1.2 mol % (about 0.3 wt %) to about 16.5 mol % (about 4wt %). In particular embodiments, the amount of manganese may range fromabout 2 mol % (about 0.5 wt %) to 13.4 mol % (about 3.3 wt %), or fromabout 2 mol % to 12.2 mol % (about 3 wt %), or from about 2 mol % to11.2 mol % (about 2.76 wt %), or from about 2 mol % to about 10 mol %(about 2.5 wt %), or from about 2 mol % to 5.5 mol % (about 1.4 wt %),or from about 2 mol % to about 3.0 mol % (about 0.75 wt %).

A process according to the present invention includes gradually adding afirst solution that contains aqueous HF and a source of M and a secondsolution that contains a source of Mn to a reactor in the presence of asource of A. Volume of the product liquor in the reactor is maintainedat an equilibrium level by discharging the product liquor at about thesame rate that feed solutions are added to the reactor. Feed solutionsinclude at least the first and second solutions, along with othersolutions that may be added to the reactor before or during thedischarging. In some embodiments, the feed solutions may be added to thereactor during an initial period when the reactor is filled to anequilibrium volume without discharging the product liquor. Theequilibrium volume is the volume that remains constant while the productliquor is discharged, and is approximately equal to the amount of feedsolutions that are added to the reactor in five minutes, particularly inthree minutes, more particularly in two minutes, and even moreparticularly in one minute. The equilibrium volume may be less than 35%of the total volume of all feed solutions, particularly less than 25% ofthe total volume of all feed solutions, and more particularly less than15% of the total volume of all feed solutions. In embodiments where thetotal amount of feed solution is about 1000 ml, the equilibrium volumemay range from about 70-200 ml, particularly from about 100-150 mi.Volume of the product liquor remains constant from the time thatdischarging of the product liquor begins until the discharging isdiscontinued, or until addition of all feeds is complete or otherwisediscontinued. After discharging has begun, the rate of discharge isapproximately the same as the total rate of addition of all feeds intothe reactor so that the volume of the product liquor remainsapproximately constant during the discharge period. In the context ofthe present invention, ‘remains approximately constant’ means that thevolume of the product liquor varies less than about 50% over the timeperiod when the product liquor is being discharged, particularly about20%, and more particularly about 10%.

The reaction time, that is, the length of the addition and dischargeperiods, is not critical. In some embodiments, it may range from aboutone hour to about two hours. In some embodiments, the feed rates may beset to produce about 10 g product per minute. The feed rate, dischargerate, and equilibrium volume may be chosen so that residence time of theproduct phosphor in the reactor ranges from about 5 seconds to about 10minutes, particularly from about 30 seconds to about 5 minutes, moreparticularly about 30 seconds to about 2 minutes, even more particularlyabout one minute.

In some embodiments, the reactor may be precharged with a materialselected from HF, a source of A, preformed particles of the Mn⁺⁴ dopedphosphor, or a combination thereof. A non-solvent or antisolvent for thephosphor product may also be included in the precharge. Suitablematerials for the antisolvent include acetone, acetic acid, isopropanol,ethanol, methanol, acetonitrile, dimethyl formamide, or a combinationthereof. Alternatively, the antisolvent may be included in any of thefeed solutions, or in a separate feed solution without a source of M orMn, particularly in a feed solution that includes a source of A withouta source of M or Mn.

A process according to the present invention may minimize the amount ofraw materials used to prepare the phosphors of formula I. In particular,the amount of toxic materials such as HF used may be significantlyreduced in comparison with a batch process. Where the amount of HF isreduced, the product liquor may contain a higher level of raw materialscompared to a batch process. In many embodiments, the product liquorcontains at least 10% dissolved solids, particularly at least 19%dissolved solids, after the start of the discharge. In addition, productyields may be higher compared batch processes. For example, productyield from processes according to the present invention may be as highas 85-95%, whereas yields from batch processes are typically in therange of 60%-75%.

The first solution includes aqueous HF and a source of M. The source ofM may be a compound containing Si, having good in solubility in thesolution, for example, H₂SiF₆, Na₂SiF₆, (NH₄)₂SiF₆, Rb₂SiF₆, Cs₂SiF₆,SiO₂ or a combination thereof, particularly H₂SiF₆. Use of H₂SiF₆ isadvantageous because it has very high solubility in water, and itcontains no alkali metal element as an impurity. The source of M may bea single compound or a combination of two or more compounds. The HFconcentration in the first solution may be at least 25 wt %,particularly at least 30 wt %, more particularly at least 35 wt %. Watermay be added to the first solution, reducing the concentration of HF, todecrease particle size and improve product yield. Concentration of thematerial used as the source of M may be ≤25 wt %, particularly ≤15 wt %.

The second solution includes a source of Mn, and may also includeaqueous HF as a solvent. Suitable materials for use as the source of Mninclude for example, K₂MnF₆, KMnO₄, K₂ MnCl₆, MnF₄, MnF₃, MnF₂, MnO₂,andcombinations thereof, and, in particular, K₂MnF₆. Concentration of thecompound or compounds used as the source of Mn is not critical; and istypically limited by its solubility in the solution. The HFconcentration in the second solution may be at least 20 wt %,particularly at least 40 wt %.

The first and second solutions are added to the reactor in the presenceof a source of A while stirring the product liquor. Amounts of the rawmaterials used generally correspond to the desired composition, exceptthat an excess of the source of A may be present. Flow rates may beadjusted so that the sources of M and Mn are added in a roughlystoichiometric ratio while the source of A is in excess of thestoichiometric amount. In many embodiments, the source of A is added inan amount ranging from about 150% to 300% molar excess, particularlyfrom about 175% to 300% molar excess. For example, in Mn-doped K₂SiF₆,the stoichiometric amount of K required is 2 moles per mole of Mn-dopedK₂SiF₆, and the amount of KF or KHF₂ used ranges from about 3.5 moles toabout 6 moles of the product phosphor.

The source of A may be a single compound or a mixture of two or morecompounds. Suitable materials include KF, KHF₂, KOH, KCl, KBr, KI, KOCH₃or K₂CO₃, particularly KF and KHF₂, more particularly KHF₂. A source ofMn that contains K, such as K₂MnF₈, may be a K source, particularly incombination with KF or KHF₂. The source of A may be present in either orboth of the first and second solutions, in a third solution addedseparately, in the reactor pot, or in a combination of one or more ofthese.

After the product liquor is discharged from the reactor, the Mn⁺⁴ dopedphosphor may be isolated from the product liquor by simply decanting thesolvent or by filtration, and treated as described in U.S. Pat. No.8,252,613 or US 2015/0054400, with a concentrated solution of a compoundof formula II in aqueous hydrofluoric acid;

A¹ _(x)[MF_(y)]   II

wherein

A¹ is H, Li, Na, K, Rb, Cs, or a combination thereof;

M is Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Y, La, Nb, Ta, Bi, Gd, or acombination thereof;

x is the absolute value of the charge of the [MF_(y)] ion; and

y is 5, 6 or 7.

The compound of formula II includes at least the MF_(y) anion of thehost compound for the product phosphor, and may also include the Acation of the compound of formula I. For a product phosphor of formulaMn-doped K₂SiF₆, suitable materials for the compound of formula IIinclude H₂SiF₆, Na₂SiF, (NH₄)₂SiF, Rb₂SiF₆. Cs₂SiF₆, or a combinationthereof, particularly H₂SiF₆, K₂SiF₆ and combinations thereof, moreparticularly K₂SiF₆. The treatment solution is a saturated or nearlysaturated of the compound of formula II in hydrofluoric acid. A nearlysaturated solution contains about 1-5% excess aqueous HF added to asaturated solution. Concentration of HF in the solution ranges fromabout 25% (wt/vol) to about 70% (wt/vol), in particular from about 40%(wt/vol) to about 50% (wt/vol). Less concentrated solutions may resultin reduced performance of the phosphor. The amount of treatment solutionused ranges from about 2-30 ml/g product, particularly about 5-20 ml/gproduct, more particularly about 5-15 ml/g product.

The treated phosphor may be vacuum filtered, and washed with one or moresolvents to remove HF and unreacted raw materials. Suitable materialsfor the wash solvent include acetic acid and acetone, and combinationsthereof.

Span is a measure of the width of the particle size distribution curvefor a particulate material or powder, and is defined according toequation (1):

$\begin{matrix}{{Span} = \frac{\left( {D_{90} - D_{10}} \right)}{D_{50}}} & (1)\end{matrix}$

wherein

-   -   D₅₀ is the median particle size for a volume distribution;    -   D₉₀ is the particle size for a volume distribution that is        greater than the particle size of 90% of the particles of the        distribution; and    -   D₁₀ is the particle size for a volume distribution that is        greater than the particle size of 10% of the particles of the        distribution.        Particle size of the phosphor powder may be conveniently        measured by laser diffraction methods, and software provided        with commercial instruments can generate D₉₀. D₁₀, and D₅₀        particle size values and span of the distribution. For phosphor        particles of the present invention, D₅₀ particle size ranges        from about 10 μm to about 40 μm, particularly from about 15 μm        to about 35 μm, more particularly from about 20 μm to about 30        μm. Span of the particle size distribution may be ≤1.0,        particularly ≤0.9, more particularly ≤0.8, and even more        particularly ≤0.7. Particle size may be controlled by adjusting        flow rates, reactant concentrations, and equilibrium volume of        the product liquor.

After the product phosphor is isolated from the product liquor, treatedand dried, it may be annealed to improve stability as described in U.S.Pat. No. 8,906,724. In such embodiments, the product phosphor is held atan elevated temperature, while in contact with an atmosphere containinga fluorine-containing oxidizing agent. The fluorine-containing oxidizingagent may be F₂, HF, SF₆, BrF₅, NH₄HF₂, NH₄F, KF, AlF₃, SbF₅, ClF₃,BrF₃, KrF₂, XeF₂, XeF₄, NF₃, SiF₄, PbF₂, ZnF₂, SnF₂, CdF₂ or acombination thereof. In particular embodiments, the fluorine-containingoxidizing agent is F₂. The amount of oxidizing agent in the atmospheremay be varied to obtain the color stable phosphor, particularly inconjunction with variation of time and temperature. Where thefluorine-containing oxidizing agent is F₂, the atmosphere may include atleast 0.5% F₂, although a lower concentration may be effective in someembodiments. In particular the atmosphere may include at least 5% F₂ andmore particularly at least 20% F₂. The atmosphere may additionallyinclude nitrogen, helium, neon, argon, krypton, xenon, in anycombination with the fluorine-containing oxidizing agent. In particularembodiments, the atmosphere is composed of about 20% F₂ and about 80%nitrogen.

The temperature at which the phosphor is contacted with thefluorine-containing oxidizing agent is any temperature in the range fromabout 200° C. to about 700° C., particularly from about 350° C. to about600° C. during contact, and in some embodiments from about 500° C. toabout 600° C. The phosphor is contacted with the oxidizing agent for aperiod of time sufficient to convert it to a color stable phosphor. Timeand temperature are interrelated, and may be adjusted together, forexample, increasing time while reducing temperature, or increasingtemperature while reducing time. In particular embodiments, the time isat least one hour, particularly for at least four hours, moreparticularly at least six hours, and most particularly at least eighthours.

After holding at the elevated temperature for the desired period oftime, the temperature in the furnace may be reduced at a controlled ratewhile maintaining the oxidizing atmosphere for an initial coolingperiod. After the initial cooling period, the cooling rate may becontrolled at the same rate or a different rate, or may be uncontrolled.In some embodiments, the cooling rate is controlled at least until atemperature of 200° C. is reached. In other embodiments, the coolingrate is controlled at least until a temperature at which it is safe topurge the atmosphere is reached. For example, the temperature may bereduced to about 50° C. before a purge of the fluorine atmospherebegins. Reducing the temperature at a controlled rate of ≤5° C. perminute may yield a phosphor product having superior properties comparedto reducing the temperature at a rate of ≤10° C./minute. In variousembodiments, the rate may be controlled at ≤5° C. per minute,particularly at ≤3° C. per minute, more particularly at a rate of ≤1° C.per minute.

The period of time over which the temperature is reduced at thecontrolled rate is related to the contact temperature and cooling rate.For example, when the contact temperature is 540° C. and the coolingrate is 10° C./minute, the time period for controlling the cooling ratemay be less than one hour, after which the temperature may be allowed tofall to the purge or ambient temperature without external control. Whenthe contact temperature is 540° C. and the cooling rate is ≤5° C. perminute, then the cooling time may be less than two hours. When thecontact temperature is 540′C and the cooling rate is ≤3° C. per minute,then the cooling time may be less than three hours. When the contacttemperature is 540° C. and the cooling rate is ≤1° C. per minute, thenthe cooling time is may be less than four hours. For example, thetemperature may be reduced to about 200° C. with controlled cooling,then control may be discontinued. After the controlled cooling period,the temperature may fall at a higher or lower rate than the initialcontrolled rate.

The manner of contacting the phosphor with the fluorine-containingoxidizing agent is not critical and may be accomplished in any waysufficient to convert the phosphor to a color stable phosphor having thedesired properties. In some embodiments, the chamber containing thephosphor may be dosed and then sealed such that an overpressure developsas the chamber is heated, and in others, the fluorine and nitrogenmixture is flowed throughout the anneal process ensuring a more uniformpressure. In some embodiments, an additional dose of thefluorine-containing oxidizing agent may be introduced after a period oftime.

The annealed phosphor may be treated with a saturated or nearlysaturated solution of a composition of formula II in aqueoushydrofluoric acid, as described in U.S. Pat. No. 8,252,613. The amountof treatment solution used ranges from about 10 ml/g product to 20 ml/gproduct, particularly about 10 ml/g product. The treated annealedphosphor may be isolated by filtration, washed with solvents such asacetic acid and acetone to remove contaminates and traces of water, andstored under nitrogen.

Any numerical values recited herein include all values from the lowervalue to the upper value in increments of one unit provided that thereis a separation of at least 2 units between any lower value and anyhigher value. As an example, if it is stated that the amount of acomponent or a value of a process variable such as, for example,temperature, pressure, time and the like is, for example, from 1 to 90,preferably from 20 to 80, more preferably from 30 to 70, it is intendedthat values such as 15 to 85, 22 to 68, 43 to 51, 30 to 32 etc. areexpressly enumerated in this specification. For values which are lessthan one, one unit is considered to be 0.0001, 0.001, 0.01 or 0.1 asappropriate. These are only examples of what is specifically intendedand all possible combinations of numerical values between the lowestvalue and the highest value enumerated are to be considered to beexpressly stated in this application in a similar manner.

A lighting apparatus or light emitting assembly or lamp 10 according toone embodiment of the present invention is shown in FIG. 1. Lightingapparatus 10 includes a semiconductor radiation source, shown as lightemitting diode (LED) chip 12, and leads 14 electrically attached to theLED chip. The leads 14 may be thin wires supported by a thicker leadframe(s) 16 or the leads may be self-supported electrodes and the leadframe may be omitted. The leads 14 provide current to LED chip 12 andthus cause it to emit radiation.

The lamp may include any semiconductor blue or UV light source that iscapable of producing white light when its emitted radiation is directedonto the phosphor. In one embodiment, the semiconductor light source isa blue emitting LED doped with various impurities. Thus, the LED maycomprise a semiconductor diode based on any suitable III-V, II-VI orIV-IV semiconductor layers and having an emission wavelength of about250 to 550 nm. In particular, the LED may contain at least onesemiconductor layer comprising GaN, ZnSe or SiC. For example, the LEDmay comprise a nitride compound semiconductor represented by the formulaIn_(i)Ga_(j)Al_(k)N (where 0≤i; 0≤j; 0≤k and I+j+k=1) having an emissionwavelength greater than about 250 nm and less than about 550 nm. Inparticular embodiments, the chip is a near-uv or blue emitting LEDhaving a peak emission wavelength from about 400 to about 500 nm. SuchLED semiconductors are known in the art. The radiation source isdescribed herein as an LED for convenience. However, as used herein, theterm is meant to encompass all semiconductor radiation sourcesincluding, e.g., semiconductor laser diodes. Further, although thegeneral discussion of the exemplary structures of the inventiondiscussed herein is directed toward inorganic LED based light sources,it should be understood that the LED chip may be replaced by anotherradiation source unless otherwise noted and that any reference tosemiconductor, semiconductor LED, or LED chip is merely representativeof any appropriate radiation source, including, but not limited to,organic light emitting diodes.

In lighting apparatus 10, phosphor composition 22 is radiationallycoupled to the LED chip 12. Radiationally coupled means that theelements are associated with each other so radiation from one istransmitted to the other. Phosphor composition 22 is deposited on theLED 12 by any appropriate method. For example, a water based suspensionof the phosphor(s) can be formed, and applied as a phosphor layer to theLED surface. In one such method, a silicone slurry in which the phosphorparticles are randomly suspended is placed around the LED. This methodis merely exemplary of possible positions of phosphor composition 22 andLED 12. Thus, phosphor composition 22 may be coated over or directly onthe light emitting surface of the LED chip 12 by coating and drying thephosphor suspension over the LED chip 12. In the case of asilicone-based suspension, the suspension is cured at an appropriatetemperature. Both the shell 18 and the encapsulant 20 should betransparent to allow white light 24 to be transmitted through thoseelements. Although not intended to be limiting, in some embodiments, themedian particle size of the phosphor composition ranges from about 1 toabout 50 microns, particularly from about 15 to about 35 microns.

In other embodiments, phosphor composition 22 is interspersed within theencapsulant material 20, instead of being formed directly on the LEDchip 12. The phosphor (in the form of a powder) may be interspersedwithin a single region of the encapsulant material 20 or throughout theentire volume of the encapsulant material. Blue light emitted by the LEDchip 12 mixes with the light emitted by phosphor composition 22, and themixed light appears as white light. If the phosphor is to beinterspersed within the material of encapsulant 20, then a phosphorpowder may be added to a polymer or silicone precursor, loaded aroundthe LED chip 12, and then the polymer precursor may be cured to solidifythe polymer or silicone material. Other known phosphor interspersionmethods may also be used, such as transfer loading.

In some embodiments, the encapsulant material 20 is a silicone matrixhaving an index of refraction R, and, in addition to phosphorcomposition 22, contains a diluent material having less than about 5%absorbance and index of refraction of R±0.1. The diluent material has anindex of refraction of ≤1.7, particularly ≤1.6, and more particularly≤1.5. In particular embodiments, the diluent material is of formula II,and has an index of refraction of about 1.4. Adding an opticallyinactive material to the phosphor/silicone mixture may produce a moregradual distribution of light flux through the phosphor/encapsulantmixture and can result in less damage to the phosphor. Suitablematerials for the diluent include fluoride compounds such as LiF, MgF₂,CaF₂, SrF₂, AlF₃, K₂NaAlF₆, KMgF₃, CaLiAlF₆, K₂LiAlF₆, and K₂SiF₆, whichhave index of refraction ranging from about 1.38 (AlF₃ and K₂NaAlF₆) toabout 1.43 (CaF₂), and polymers having index of refraction ranging fromabout 1.254 to about 1.7. Non-limiting examples of polymers suitable foruse as a diluent include polycarbonates, polyesters, nylons,polyetherimides, polyetherketones, and polymers derived from styrene,acrylate, methacrylate, vinyl, vinyl acetate, ethylene, propylene oxide,and ethylene oxide monomers, and copolymers thereof, includinghalogenated and unhalogenated derivatives. These polymer powders can bedirectly incorporated into silicone encapsulants before silicone curing.

In yet another embodiment, phosphor composition 22 is coated onto asurface of the shell 18, instead of being formed over the LED chip 12.The phosphor composition is preferably coated on the inside surface ofthe shell 18, although the phosphor may be coated on the outside surfaceof the shell, if desired. Phosphor composition 22 may be coated on theentire surface of the shell or only a top portion of the surface of theshell. The UV/blue light emitted by the LED chip 12 mixes with the lightemitted by phosphor composition 22, and the mixed light appears as whitelight. Of course, the phosphor may be located in any two or all threelocations or in any other suitable location, such as separately from theshell or integrated into the LED.

FIG. 2 illustrates a second structure of the system according to thepresent invention. Corresponding numbers from FIGS. 1-4 (e.g. 12 inFIGS. 1 and 112 in FIG. 2) relate to corresponding structures in each ofthe figures, unless otherwise stated. The structure of the embodiment ofFIG. 2 is similar to that of FIG. 1, except that the phosphorcomposition 122 is interspersed within the encapsulant material 120,instead of being formed directly on the LED chip 112. The phosphor (inthe form of a powder) may be interspersed within a single region of theencapsulant material or throughout the entire volume of the encapsulantmaterial. Radiation (Indicated by arrow 126) emitted by the LED chip 112mixes with the light emitted by the phosphor 122, and the mixed lightappears as white light 124. If the phosphor is to be interspersed withinthe encapsulant material 120, then a phosphor powder may be added to apolymer precursor, and loaded around the LED chip 112. The polymer orsilicone precursor may then be cured to solidify the polymer orsilicone. Other known phosphor interspersion methods may also be used,such as transfer molding.

FIG. 3 illustrates a third possible structure of the system according tothe present invention. The structure of the embodiment shown in FIG. 3is similar to that of FIG. 1, except that the phosphor composition 222is coated onto a surface of the envelope 218, instead of being formedover the LED chip 212. The phosphor composition 222 is preferably coatedon the inside surface of the envelope 218, although the phosphor may becoated on the outside surface of the envelope, if desired. The phosphorcomposition 222 may be coated on the entire surface of the envelope, oronly a top portion of the surface of the envelope. The radiation 226emitted by the LED chip 212 mixes with the light emitted by the phosphorcomposition 222, and the mixed light appears as white light 224. Ofcourse, the structures of FIGS. 1-3 may be combined, and the phosphormay be located in any two or all three locations, or in any othersuitable location, such as separately from the envelope, or integratedinto the LED.

In any of the above structures, the lamp may also include a plurality ofscattering particles (not shown), which are embedded in the encapsulantmaterial. The scattering particles may comprise, for example, alumina ortitania. The scattering particles effectively scatter the directionallight emitted from the LED chip, preferably with a negligible amount ofabsorption.

As shown in a fourth structure in FIG. 4, the LED chip 412 may bemounted in a reflective cup 430. The cup 430 may be made from or coatedwith a dielectric material, such as alumina, titania, or otherdielectric powders known in the art, or be coated by a reflective metal,such as aluminum or silver. The remainder of the structure of theembodiment of FIG. 4 is the same as those of any of the previousfigures, and can include two leads 416, a conducting wire 432, and anencapsulant material 420. The reflective cup 430 is supported by thefirst lead 416 and the conducting wire 432 is used to electricallyconnect the LED chip 412 with the second lead 416.

Another structure (particularly for backlight applications) is a surfacemounted device (“SMD”) type light emitting diode 550, e.g. asillustrated in FIG. 5. This SMD is a “side-emitting type” and has alight-emitting window 552 on a protruding portion of a light guidingmember 554. An SMD package may comprise an LED chip as defined above,and a phosphor material that is excited by the light emitted from theLED chip. Other backlight devices include, but are not limited to, TVs,computers, smartphones, tablet computers and other handheld devices thathave a display including a semiconductor light source; and a colorstable Mn⁴⁺ doped phosphor according to the present invention.

When used with an LED emitting at from 350 to 550 nm and one or moreother appropriate phosphors, the resulting lighting system will producea light having a white color. Lamp 10 may also include scatteringparticles (not shown), which are embedded in the encapsulant material.The scattering particles may comprise, for example, alumina or titania.The scattering particles effectively scatter the directional lightemitted from the LED chip, preferably with a negligible amount ofabsorption.

In addition to the color stable Mn⁺⁴ doped phosphor, phosphorcomposition 22 may include one or more other phosphors. When used in alighting apparatus in combination with a blue or near UV LED emittingradiation in the range of about 250 to 550 nm, the resultant lightemitted by the assembly will be a white light. Other phosphors such asgreen, blue, yellow, red, orange, or other color phosphors may be usedin the blend to customize the white color of the resulting light andproduce specific spectral power distributions. Other materials suitablefor use in phosphor composition 22 include electroluminescent polymerssuch as polyfluorenes, preferably poly(9,9-dioctyl fluorene) andcopolymers thereof, such aspoly(9,9′-dioctylfluorene-co-bis-N,N′-(4-butylphenyl)diphenylamine)(F8-TFB); poly(vinylcarbazole) and polyphenylenevinylene and theirderivatives. In addition, the light emitting layer may include a blue,yellow, orange, green or red phosphorescent dye or metal complex, or acombination thereof. Materials suitable for use as the phosphorescentdye include, but are not limited to, tris(1-phenylisoquinoline) iridium(III) (red dye), tris(2-phenylpyridine) iridium (green dye) and Indium(III) bis(2-(4,6-difluorephenyl)pyridinato-N,C2) (blue dye).Commercially available fluorescent and phosphorescent metal complexesfrom ADS (American Dyes Source, Inc.) may also be used. ADS green dyesinclude ADS060GE, ADS061GE, ADS063GE, and ADS066GE, ADS078GE, andADS090GE. ADS blue dyes include ADS064BE, ADS065BE, and ADS070BE. ADSred dyes include ADS067RE, ADS068RE, ADS069RE, ADS075RE, ADS076RE,ADS067RE, and ADS077RE.

Suitable phosphors for use in phosphor composition 22 in addition to theMn^(4′+) doped phosphor include, but are not limited to:

((Sr_(1−z) (Ca, Ba, Mg, Zn)_(z))_(1−(x+w))(Li, Na, K,Rb)_(w)Ce_(x))₃(Al_(1−y)Si_(y))O_(4+y+3(x−w))F_(1−y−3(x−w)), wherein0<x≤0.10, 0≤y≤0.5, 0≤z≤0.5, 0≤w≤x;(Ca, Ce)₃Sc₂Si₃O₁₂ (CaSiG);(Sr,Ca,Ba)₃Al_(1−x)Si_(x)O_(4+x)F_(1−x):Ce³⁺ (SASOF));(Ba,Sr,Ca)₅(PO₄)₃(Cl,F,Br,OH):Eu²⁺,Mn²⁺; (Ba,Sr.Ca)BPO₅:Eu²⁺,Mn²⁺;(Sr,Ca)₁₀(PO₄)₆*□B₂O₃:Eu²⁺ (wherein 0<□≤1);Sr₂Si₃O₈*2SrCl₂:Eu²⁺; (Ca,Sr,Ba)₃MgSi₂O₈:Eu²⁺,Mn²⁺; BaAl₈O₁₃:Eu²⁺;2SrO*0.84P₂O₅*0.16B₂O₃:Eu²⁺; (Ba,Sr,Ca)MgAl₁₀O₁₇:Eu²⁺,Mn²⁺;(Ba,Sr,Ca)Al₂O₄:Eu²⁺;(Y,Gd,Lu,Sc,La)BO₃:Ce³⁺,Tb³⁺; ZnS:Cu⁺,Cl⁻; ZnS:Cu⁺,Al³⁺; ZnS:Ag⁺,Cl⁻;ZnS:Ag⁺,Al³⁺;(Ba,Sr,Ca)₂Si_(1−□)O_(4−2□):Eu²⁺ (wherein −0.2≤□≤0.2);(Ba,Sr,Ca)₂(Mg,Zn)Si₂O₇:Eu²⁺;(Sr,Ca,Ba)(Al,Ga,In)₂S₄:Eu²⁺;(Y,Gd,Tb,La,Sm,Pr,Lu)₃(Al,Ga)_(5−□)O_(12−3/2□):Ce³⁺ (wherein 0≤□≤0.5);(Y,Gd,Lu,Tb)₃(Al,Ga)₅O₁₂:Ce³⁺;(Ca,Sr)₈(Mg,Zn)(SiO₄)₄Cl₂:Eu²⁺,Mn²⁺; Na₂Gd₂B₂O₇:Ce³⁺,Tb³⁺;(Sr,Ca,Ba,Mg,Zn)₂P₂O₇:Eu²⁺,Mn²⁺;(Gd,Y,Lu,La)₂O₃:Eu³⁺,Bi³⁺; (Gd,Y,Lu,La)₂O₂S:Eu³⁺,Bi³⁺;(Gd,Y,Lu,La)VO₄:Eu³⁺,Bi³⁺;(Ca,Sr)S:Eu²⁺,Ce³⁺; SrY₂S₄:Eu²⁺; CaLa₂S₄:Ce³⁺;(Ba,Sr,Ca)MgP₂O₇:Eu²⁺,Mn²⁺;(Y,Lu)₂WO₆:Eu³⁺,Mo⁶⁺; (Ba,Sr,Ca)_(□)Si_(□)N_(□):Eu²⁺ (wherein 2□+4□=3□);(Ba,Sr,Ca)₂Si_(5−x)Al_(x)N_(8−x)O_(x):Eu²⁺ (wherein 0≤x≤2);Ca₃(SiO₄)Cl₂:Eu²⁺;(Lu,Sc,Y,Tb)_(2−u−v)Ce_(v)Ca_(t+u)Li_(w)Mg_(2−w)P_(w)(Si,Ge)_(3−w)O_(12−u/2)(where −0.5≤u≤1, 0<v≤0.1, and 0≤w≤0.2);(Y,Lu,Gd)_(2−□)Ca_(□)Si₄N_(6+□)C_(1−□):Ce³⁺, (wherein 0≤□≤0.5);α−SiAlON doped with Eu²⁺ and/or Ce³⁺; (Ca,Sr,Ba)SiO₂N₂:Eu²⁺,Ce³⁺;β−SiAlON:Eu²⁺, 3.5MgO*0.5MgF₂*GeO₂:Mn⁴⁺; (Sr,Ca,Ba,Mg)AlSiN₃:Eu²⁺;(Sr,Ca,Ba)₃SiO₅:Eu²⁺; Ca_(1−c−f)Ce_(c)Eu_(f)Al_(1+c)Si_(1−c)N₃, (where0≤c≤0.2, 0≤f≤0.2);Ca_(1−h−r)Ce_(h)Eu_(r)Al_(1−h)(Mg,Zn)_(h)SiN₃, (where 0≤h≤0.2, 0≤r≤0.2);Ca_(1−2s−t)Ce₅(Li,Na)₅Eu_(t)AlSiN₃, (where 0≤s≤0.2, 0≤f≤0.2, s+t>0); andCa_(1−□−□−ϕ)Ce_(□)(Li,Na)_(□)Eu_(□)Al_(1+□−□)Si_(1−□+□)N₃, (where0≤□≤0.2, 0≤□≤0.4, 0≤□≤0.2).

In particular, phosphor composition 22 may include one or more phosphorsthat result in a green spectral power distribution under ultraviolet,violet, or blue excitation. In the context of the present invention,this is referred to as a green phosphor or green phosphor material. Thegreen phosphor may be a single composition or a blend that emits lightin a green to yellow-green to yellow range, such as cerium-doped yttriumaluminum garnets, more particularly (Y,Gd,Lu,Tb)₃(Al,Ga)₅O₁₂:Ce³⁺. Thegreen phosphor may also be a blend of blue- and red-shifted garnetmaterials. For example, a Ce³⁺-doped garnet having blue shifted emissionmay be used in combination with a Ce³⁺-doped garnet that has red-shiftedemission, resulting in a blend having a green spectral powerdistribution. Blue- and red-shifted garnets are known in the art. Insome embodiments, versus a baseline Y₃Al₅O₁₂:Ce³⁺ phosphor, ablue-shifted garnet may have Lu³⁺ substitution for Y³⁺, Ga³⁺substitution for Al³⁺, or lower Ce³⁺ doping levels in a Y₃Al₅O₁₂:Ce³⁺phosphor composition. A red-shifted garnet may have Gd³⁺/Tb³⁺substitution for Y³⁺ or higher Ce³⁺ doping levels. An example of a greenphosphor that is particularly useful for display application isβ-SiAlON.

The ratio of each of the individual phosphors in the phosphor blend mayvary depending on the characteristics of the desired light output. Therelative proportions of the individual phosphors in the variousembodiment phosphor blends may be adjusted such that when theiremissions are blended and employed in an LED lighting device, there isproduced visible light of predetermined x and y values on the CIEchromaticity diagram. As stated, a white light is preferably produced.This white light may, for instance, may possess an x value in the rangeof about 0.20 to about 0.55, and a y value in the range of about 0.20 toabout 0.55. As stated, however, the exact identity and amounts of eachphosphor in the phosphor composition can be varied according to theneeds of the end user. For example, the material can be used for LEDsintended for liquid crystal display (LCD) backlighting. In thisapplication, the LED color point would be appropriately tuned based uponthe desired white, red, green, and blue colors after passing through anLCD/color filter combination. The list of potential phosphor forblending given here is not meant to be exhaustive and these Mn⁴⁺-dopedphosphors can be blended with various phosphors with different emissionto achieve desired spectral power distributions.

In some embodiments, lighting apparatus 10 has a color temperature lessthan or equal to 4200° K, and phosphor composition 22 includes a redphosphor consisting of a color stable Mn⁴⁺ doped phosphor of formula I.That is, the only red phosphor present in phosphor composition 22 is thecolor stable Mn⁺⁴ doped phosphor, in particular, the phosphor isK₂SiF₆:Mn⁴⁺. The composition may additionally include a green phosphor.The green phosphor may be a C³⁺-doped garnet or blend of garnets,particularly a Ce³⁺-doped yttrium aluminum garnet, and moreparticularly, YAG having the formula (Y,Gd,Lu,Tb)₃(Al,Ga)₅O₁₂:Ce³⁺. Whenthe red phosphor is K₂SiF₆:Mn⁴⁺, the mass ratio of the red phosphor tothe green phosphor material may be less than 3.3, which may besignificantly lower than for red phosphors of similar composition, buthaving lower levels of the Mn dopant.

The color stable Mn⁺⁴ doped phosphors of the present invention may beused in applications other than those described above. For example, thematerial may be used as a phosphor in a fluorescent lamp, in a cathoderay tube, in a plasma display device or in a liquid crystal display(LCD). The material may also be used as a scintillator in anelectromagnetic calorimeter, in a gamma ray camera, in a computedtomography scanner or in a laser. These uses are merely exemplary andnot limiting.

EXAMPLES Comparative Examples 1 and 2: Preparation of Mn⁺⁴ Doped K₂SiF₆by Batch Process

Amounts and distribution of starting materials among Beakers A-C areshown in Table 1. Beaker A was stirred aggressively, and the contents ofbeaker B were added thereto dropwise over the course of about fiveminutes. Dropwise addition of the contents of beaker C to beaker A wasstarted about one minute after the contents of beaker B was started andcontinued over the course of about four minutes. The precipitate wasdigested for 5 minutes and the stirring was stopped. The supernatant wasdecanted, and the precipitate was vacuum filtered, rinsed once withacetic acid and twice with acetone, and then dried under vacuum. Thedried powder was sifted through a 170-mesh screen, and annealed under a20% F₂/80% nitrogen atmosphere for 8 hour at 540° C. The annealedphosphor was washed with a solution of 49% HF saturated with K₂SiF₆,dried under vacuum and sifted through a 170-mesh screen.

TABLE 1 Batch Process Raw Materials Solution B Solution C Comp. SolutionA HF H₂SiF₆ HF HF Ex. KF KH₂F K₂MnF₆ (49%) (35%) (49%) K₂MnF₆ (49%) no.(g) (g) (g) (mL) (mL) (mL) (g) (mL) 1 8.1 0.18 65 1.5 60 0.18 21070913AT 2 16.2 0.37 130 30 120 0.37 42 071213AT

Examples 1-6: Preparation of Mn⁴⁺ Doped K₂SiF₆ by Continuous FlowProcess Procedure

A 2000 ml separatory funnel used as a reaction vessel was stirred at arate of about 300 RPM. Three peristaltic pumps were used to maintaintight control over all flow rates. Flow rates were set between 15-40mL/min for solution A and solution B and between 30-100 mL/min forsolution 3. Amounts and distribution of starting materials amongSolutions A-C for Examples 1-6 are shown in Table 2.

The reaction vessel was filled to an equilibrium volume of 100-200 mLand then the stopcock was opened such that the combined flow rate of thethree flows was equal to the flow rate out of the drain. The volume inthe reaction vessel was maintained within about 5-10% of the initialequilibrium volume from the time the reaction vessel started to drainuntil the reaction was complete. The combined flow rate of the threesolutions ranged from 80-130 mL/minute. The residence time of theproduct phosphor in the reaction vessel ranged from 30 seconds to 2minutes.

The outflow from the reaction vessel was directed to a receiving vessel,where the solvent was decanted from the product. A nearly saturatedsolution of K₂SiF₆ in 49% HF was prepared by adding 4.2 g K₂SiF₆ per 100ml 49% HF to form a suspension which was vacuum filtered to removeexcess solids. Approximately 2 vol % 49% HF was added to the saturatedsolution, to form a nearly saturated solution. The slurry was mixed with500 ml of the nearly saturated at a rate of about 6 ml solution per 1 gproduct and stirred for about 20 minutes. The treated product was vacuumfiltered, rinsed once with acetic acid and three times with acetone, andthen dried under vacuum. The dried powder was sifted through a 170-meshscreen, and annealed under an atmosphere composed of 20% F₂/80% nitrogenfor about 8 hours at 540° C. The slurry was mixed with 1000 ml of asolution of 49% HF nearly saturated with K₂SiF₆ at a rate of about 12 mlsolution per 1 g product and stirred for about 20 minutes. The treatedproduct was vacuum filtered, rinsed once with acetic acid and threetimes with acetone, and then dried under vacuum. The dried powder wassifted through a 170-mesh screen, and annealed under an atmospherecomposed of 20% F₂/80% nitrogen for about 8 hours at 540° C.

TABLE 2 Solution A Solution B Solution C HF HF H₂SiF₆ HF H₂SiF₆: KF KH₂F(49%) K₂MnF₆ (49%) (35%) (49%) HF Example no. (g) (g) (mL) (g) (mL) (mL)(mL) Ratio 1 24 63 3.3 55 27 70 1:2.5 2 34 51 3 50 28 56 1:2.0C072215B-T 3 31 63 2.5 42 2 0 1:0   F061715A-T 4 31 63 2.5 42 28 701:2.5 F061715B-T 5 31 63 2.5 42 28 35  1:1.25 F061715C-T 6 149.6 264 12202 112 240  1:2.14 C092215A-TGAT 7 151.8 268 13.2 218 108.3 232  1:2.14C092215B-TGAT 8 120.6 181 16 240 105 225  1:2.14 C092215C-TGAT

Sample tapes were prepared by mixing 500 mg of the phosphor with 1.50 gSylgard 184 silicone. The mixture was degassed in a vacuum chamber forabout 15 minutes. The mixture (0.70 g) was poured into a disc-shapedtemplate (28.7 mm diameter and 0.79 mm thick) and baked for 30 minutesat 90° C. The sample was cut into squares of size approximately 5 mm×5mm for testing.

QE of the phosphors was measured at excitation wavelength of 450 nm QEof the phosphors was measured at excitation wavelength of 450 nm and isreported relative to a reference sample of Mn⁴⁺ doped K₂SiF₆ with 0.68%Mn and a particle size of 28 microns from a commercial source. Lifetimewas determined using an Edinburgh FS900 Spectrometer by fitting a singleexponential decay to the measured data between 1.4 ms and 67 ms afterexcitation. Particle size data was obtained using a Horiba LA-960 LaserScattering Particle Size Distribution Analyzer. The amount of manganeseincorporated in the phosphor was determined by inductively coupledplasma mass spectrometry (ICP-MS), and is reported as weight %, based ontotal weight of the phosphor material. Results are shown in Table 3.

TABLE 3 QE, D₁₀, D₅₀, D₉₀, Mn, Example no. % Lifetime μm μm μm Span %Comp. ex. 1 103.8 8.540 15 29 50 1.20 0.84 Comp. ex. 2 103.4 NA 11 43 781 0.56 1 100.2 8.391 21 31 44 0.74 2.55 2 103.1 8.445 14 22 33 0.86 1.343 49.5 6.900 10 15 23 0.87 1.73 4 100.5 8.388 18 27 40 0.81 2.1 5 92.58.205 10 15 22 0.80 1.86 6 101.1 8.408 21 29 39 0.64 2.35 7 99.7 8.37 2233 49 0.81 2.58 8 99.7 8.322 23 32 42 0.59 3.06

For Comparative Examples 1 and 2, it can be seen that particle size andspan increased at the larger scale; D₁₀, D₅₀, and D₉₀ increased by21%-25%, and the span of the distribution increased from 1.20 to 1.54.In contrast, for the phosphors of Examples 1-6, span was dramaticallynarrower than for the batch samples, ranging between 0.74 and 0.87, withD₅₀ ranging between 15 μm and 31 μm. For Examples 3 and 5, QE of thephosphors was reduced compared to that of the phosphors of Examples 1,2, and 4, which used higher amounts of HF in the process. Examples 6-8demonstrate that a narrow particle size distribution can be achieved athigher dopant levels.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

1-10. (canceled)
 11. A Mn⁺⁴ doped phosphor of formula I comprising apopulation of particles having a particle size distribution comprisingD₅₀ particle size ranging from about 10 μm to about 40 μm and a spanless than 1.1;A_(x)[MF_(y)]:Mn⁺⁴   I wherein A is Li, Na, K, Rb, Cs, or a combinationthereof; M is Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Y, La, Nb, Ta, Bi, Gd,or a combination thereof; x is the absolute value of the charge of the[MF_(y)] ion; and y is 5, 6 or
 7. 12. A Mn⁺⁴ doped phosphor according toclaim 11, wherein the D₅₀ ranges from about 15 μm to about 35 μm.
 13. AMn⁺⁴ doped phosphor according to claim 11, wherein the span is lessthan
 1. 14. A Mn⁺⁴ doped phosphor according to claim 11, wherein thespan is less than 0.9.
 15. A Mn⁺⁴ doped phosphor according to claim 11,wherein the span is less than 0.8.
 16. A lighting apparatus comprising aMn⁺⁴ doped phosphor according to claim
 11. 17. A backlight devicecomprising a Mn⁺⁴ doped phosphor according to claim
 11. 18-22.(canceled)